In Ethernet network architectures, devices connected to the network compete for the ability to use shared telecommunications paths at any given time. Where multiple bridges or nodes are used to interconnect network segments, multiple potential paths to the same destination often exist. The benefit of this architecture is that it provides path redundancy between bridges and permits capacity to be added to the network in the form of additional links. However to prevent loops from being formed, a spanning tree was generally used to restrict the manner in which traffic was broadcast on the network. Since routes were learned by broadcasting a frame and waiting for a response, and since both the request and response would follow the spanning tree, most if not all of the traffic would follow the links that were part of the spanning tree. This often led to over-utilization of the links that were on the spanning tree and non-utilization of the links that weren't part of the spanning tree.
To overcome some of the limitations inherent in Ethernet networks, a link state protocol controlled Ethernet network was disclosed in U.S. patent application Ser. No. 11/537,775, filed Oct. 2, 2006, entitled “Provider Link State Bridging,” the content of which is hereby incorporated herein by reference. As described in greater detail in that application, the nodes in a link state protocol controlled Ethernet network exchange hello messages to learn adjacencies of other nodes on the network, and transmit link state advertisements to enable each node on the network to build a link state database. The link state database may then be used to compute shortest paths through the network. Each node then populates a Forwarding Information Base (FIB) which will be used by the node to make forwarding decisions so that frames will be forwarded over the computed shortest path to the destination. Since the shortest path to a particular destination is always used, the network traffic will be distributed across a larger number of links and follow a more optimal path for a larger number of nodes than where a single Spanning Tree or even multiple spanning trees are used to carry traffic on the network.
When customer traffic enters a provider network, the customer MAC address (C-MAC DA) is resolved to a provider MAC address (B-MAC DA), so that the provider may forward traffic on the provider network using the provider MAC address space. Additionally, the network elements on the provider network are configured to forward traffic based on Virtual LAN ID (VID) so that different frames addressed to the same destination address but having different VIDs may be forwarded over different paths through the network. In operation, a link state protocol controlled Ethernet network may associate one VID range with shortest path forwarding, such that unicast and multicast traffic may be forwarded using a VID from that range, and traffic engineering paths may be created across the network on paths other than the shortest path, and forwarded using a second VID range. The use of Traffic Engineered (TE) paths through a link state protocol controlled Ethernet network is described in greater detail in U.S. patent application Ser. No. 11/732,381, filed Apr. 3, 2007, entitled “Engineered Paths In A Link State Protocol Controlled Ethernet Network”, the content of which is hereby incorporated herein by reference.
Large networks may be broken into smaller areas. Routing within a given area may be implemented independent of the other areas to enable the routing tables on the network elements within that area to be kept to a reasonable size and as a consequence the time to compute forwarding tables bounded as the network grows. Recognizing that some routes may need to span across multiple areas, however it may be desirable to provide a way that will enable the control planes of the multiple areas to coordinate the exchange of information to enable forwarding paths to be established across multiple network areas.